The disclosure relates to glass substrates with a modified surface layer, and more particularly to glass substrates with an alkali-containing bulk and an alkali-depleted surface layer.
Glasses formed or treated using known surface treatment (e.g., including melt-prepared glasses) often include surface layers that are at least partially crystallized or include crystallized portions, or may exhibit phase separation (i.e., a nonhomogeneous composition, typically including 5, 6-coordinated aluminum). In other known methods or applications used to modify surface layers (e.g., leaching or wet chemical treatments), the resulting surface layer includes hydrogen, which may be present in the form of H+, H3O+, H2O or combinations thereof.
Thermal poling has been utilized to modify the properties of glass. Thermal poling generally involves the application of voltage to a glass. Known uses of thermal poling include the formation of depletion layers that inhibit alkali migration in photovoltaic glasses, the formation of interfacial barrier layers between display (or alkali-free) glass and silicon, and the formation of surface texture or selective-area ion exchange through the use of patterned electrodes.
Thermal poling is also used in the art to induce second-order nonlinear properties, especially second-order nonlinear optical properties, for the purpose of creating optical switches and devices. Poling methods are also closely analogous to so-called anodic bonding, which is applied to bond alkali-containing or alkali-free glasses to other materials, especially semiconductors.
The instant disclosure discloses glass substrates having a variety of compositions in the aluminosilicate family and a surface layer with a modified composition and atomic structure. In some embodiments, the surface layer is has a reduced concentration of alkali, while the bulk of the glass substrate includes alkali. The surface layer includes an atomic structure that is believed to be substantially enriched in 3-coordinated oxygen (also referred to herein as oxygen in a 3-coordinated state or oxygen triclusters) and which enable various surface properties and performance attributes of the glass substrate. For example, the surface layer can be used to improve the corrosion resistance, diffusion barrier, hardness, elastic modulus, fatigue resistance and damage resistance (e.g., anomalous deformation) of the glass substrate.